The regulation about criteria, classification of disablement and health board reports to be given to the handicapped dated 30.3.2013 is used for determination of the hearing handicap. According to this regulation hearing thresholds at 500, 1000, 2000 and 4000Hz are measured, and hearing and general disability ratings are calculated. However, 4000Hz is the most commonly affected frequency in noise induced heaing loss and overestimation is possible. In some health systems in the United States and Europe the frequency of 3000Hz is used. In our study we aimed to examine the effect of using 4000 Hz, the frequency most commonly affected by noise induced hearing loss, on calculation of hearing and general disability rating.
Methods: Pure tone audiometry was performed on patients seen at the disability health board on 500, 1000, 2000 and 4000Hz frequencies and an additional 3000Hz . Bilateral total hearing loss and normal hearing cases were excluded. Disability ratings using 500, 1000, 2000 and 4000Hz (PTA 5124) and 500, 1000, 2000 and 3000Hz (PTA 5123) were calculated. The difference between 4000 and 3000 Hz thresholds were also calculated.
Results: 140 patients were evaluated. 49 patients who had normal hearing or bilateral total hearing loss were excluded, so a total of 91 patients were examined. The difference between 4000 and 3000 Hz thresholds was 6.31±9.56(-20 - 35) dB (Z=-2.485; p=0.013) for the right ear and 6.86±7.91(-10-25) (p=0.008;Z=-2.637) for the left ear. Disability rating was 18.17±10.91%(2-42) according to PTA 5124 and 16.74±11.04%(0-42) according to PTA 5123. The difference between the disability rating at PTA 5124 and PTA 5123 was 1.42±1.89%(-2-6) (p=0.364).
Conclusion: Using 3000Hz instead of 4000Hz resulted in no significant difference in disability rating. Using the threshold of 4000Hz does not seem to cause an overestimation of the disability rating. Further studies in patients specifically affected by noise induced hearing loss may be appropriate.